CRUCIAL MISTAKE: Ruben Tejada’s throwing error in the eighth inning helped cost the Mets a win against the Rockies in the second game of Tuesday night’s doubleheader. Photo: AP

DENVER — No thinking allowed.

That is David Wright’s advice for Ruben Tejada, as the Mets shortstop tries to shake a defensive slump in which he has committed six errors in 13 games. Maybe the costliest of those errors occurred in the nightcap of Tuesday’s doubleheader against the Rockies, when Tejada made a wild throw to first base in the eighth inning on Michael Cuddyer’s grounder. Two runs scored on a play that should have ended the inning, tying the game before the Mets lost 9-8 in 10 innings.

Four of Tejada’s errors this season have been on throws.

“He’s putting a lot of pressure on himself,” Wright said. “You can just tell he’s thinking about a lot of things instead of just playing. The ones that are reactionary plays, he’s fine with. It’s the one’s he’s got to think about. I’ve been there. Everybody has been there.”

The Mets have little choice but to stick with Tejada through his troubles. The team isn’t even carrying a legitimate backup on the 25-man roster — Justin Turner and Jordany Valdespin have almost no experience at the position — and Triple-A shortstop Omar Quintanilla is viewed as a good glove option with limited offensive potential.

At least Tejada hasn’t been a disaster at the plate. He’s batting .271 with a .352 on-base percentage to start the season.

Manager Terry Collins said it’s too early to be concerned about Tejada’s defensive lapses.

“I’ve seen this guy play too much, and I’ve never seen this — never,” Collins said after last night’s scheduled game was postponed by snow. “So had I seen this in the past at some time I may be concerned about it, but I’m just saying the conditions have been unfavorable for what’s going on here.”

But Tejada said the cold conditions in which the Mets have played — including at Citi Field before heading to Minnesota and Colorado on this road trip — can’t be used as a crutch.

“It’s hard, but it’s no excuse,” Tejada said. “I have to do something to try and stay ready for every ground ball. Every throw is critical.”

Collins said it’s hard to pinpoint Tejada’s problem because there hasn’t been a common dominator.

“Last week in New York, every bad throw he made was down,” Collins said. “The ball [Tuesday] night just got away.”

Collins said he doubts Tejada has a case of the yips, because his throws remain consistently strong, even when they are off target. The manager said the telltale sign of a mental block is lobbing the ball.

But Wright has endured enough defensive slumps to know the mental aspect becomes an issue.

“You start outthinking instead of just doing what you’ve done your entire life playing baseball,” Wright said. “And all of a sudden you catch it and start thinking about, ‘I need to do this mechanically, I need to do this with my feet.’ Instead of just doing it. I think that’s where Ruben is at right now.

“It just takes a couple of those reactionary plays where you just make the play and it happens and you just put your mind at ease and you start rolling from there.”